Systems and Methods to Increase the Reliability and the Service Life Time of Photovoltaic (PV) Modules

ABSTRACT

An apparatus may determine a parameter related to a voltage value at a midpoint terminal of a system power device, and may adjust a voltage applied to a second terminal of the system power device based on the parameter and a reference value. The second terminal may be different from the midpoint terminal.

RELATED APPLICATIONS

This application claims priority to U.S. provisional application Ser.No. 62/669,499, filed May 10, 2018, entitled “Systems and methods toincrease the reliability and the service life time of photovoltaic (PV)modules.” The content of the foregoing application is incorporated byreference in its entirety.

BACKGROUND

A possible way of reducing the costs of photovoltaic systems is toincrease the reliability and the service lifetime of photovoltaic (PV)modules. A PV module failure may be caused by an effect that degeneratesthe module power that may or may not be reversed by normal operationand/or creates a safety issue. The underperformance of siliconwafer-based PV systems may be due to an effect termed “polarization”where n-type cells over time developed voltage induced powerdegeneration at a positive polarity from cells to ground. Conversely,several different module types with p-type cells may degenerate innegative polarity from cells to ground. Power losses in PV modules maybe more pronounced the higher the voltage is. In crystalline siliconwafer-based PV modules, a reversible polarization effect may be appliedfor p-type and n-type cells, at negative and positive voltages,respectively.

SUMMARY

The following summary is a short summary of some of the inventiveconcepts for illustrative purposes only and is not intended to limit orconstrain the features and examples in the detailed description. Oneskilled in the art will recognize other novel combinations and featuresfrom the detailed description.

A requirement of a power system may be to ensure an efficient deliveryof power to a load. To enable the efficient delivery, monitoring of thepower in terms of sensed voltages, currents and impedance by sensors ofinterconnected components of the power system may be conveyed to acontroller for an analysis. The result of the analysis may be to sendcontrol signals responsive to the analysis to the interconnectedcomponents of the power system. The interconnected components mayinclude sources of direct current (DC) power such as photovoltaic (PV)generators, wind power turbines, DC generators and/or batteries. DC toDC converters may be connected to the DC sources and the outputs of theDC to DC converters may be connected together to provide multiplestrings which may be connected across a load. The load may be a DC toalternating current (AC) inverter which has an output which may beconnected to a utility grid or a localized grid which may be separate tothe utility grid.

The control signals as a result of the analysis may ensure that theinterconnected components of the power system perform in concert toensure efficient delivery of power to a load for example. The conveyingand monitoring of the applied control signals may provide a dynamic wayof providing efficient delivery of power to a load by use of controlmethods (e.g., adaptive and/or robust control methods). The use ofcontrol methods (e.g., adaptive and/or robust control methods) may beincluded in a power system which may include a source of direct current(DC) voltage supplied across a first output terminal and a second outputterminal. A DC to AC inverter may include a first input terminal and asecond input terminal. The first input terminal and the second inputterminal may be connectable to the first output terminal and the secondoutput terminal respectively. The DC to AC inverter may further includea third input terminal. The system may include a converter adaptable toconvert a source of power on a third input terminal and a fourth inputterminal to a DC output voltage on a third output terminal. The thirdinput terminal and/or the fourth input terminal may be connectable to aground. The third output terminal may be connectable to the first inputterminal and/or the second input terminal. The voltage of the firstinput terminal and/or the second input terminal may be configurableand/or controllable to be substantially above or below the potential ofthe ground. The third output terminal may be connectable to the thirdinput terminal. The source of power may be from at least one of a DCvoltage and an AC voltage. The source of DC voltage may include a DC toDC converter with an output connected to the first output terminal andthe second output terminal and a photovoltaic panel may connect to theinput of the DC to DC converter.

The disclosure herein may include a method for a power system to providea source of DC voltage across a first output terminal and a secondoutput terminal of the source. The DC voltage may be applied to theinput of an inverter. The DC voltage may be inverted to an AC voltage bythe inverter. An electrical parameter (e.g. voltage, current, power,frequency, etc.) related to the inverting may be sensed on at least oneof the first output terminal and the second output terminal. A convertermay convert a source of power received on input terminals to a DC outputpower responsive to the sensed parameter, and one of the input terminalsof the converter may be connected to a reference terminal. The DC outputpower may be added to the source of DC voltage on at least one of thefirst output terminal and the second output terminal. A voltagepotential that may be substantially above or below a reference potentialof the reference terminal may be established and maintained at the firstoutput terminal and/or the second output terminal. The referencepotential may be a ground potential. The power source may provide powerat a DC voltage and/or at an AC voltage.

The disclosure herein may include a power system including a first groupof DC power sources, and a first group of power converters with inputsconnectable respectively to the power sources on multiple firstterminals and second terminals. The outputs of the power converters maybe connected in series between first output terminals and second outputterminals. Multiple DC to AC inverters with inputs may be connected inparallel across first output terminals and the second output terminals.A second group of power converters may be adapted to convert power frommultiple power sources on third input terminals and fourth inputterminals to DC output voltages on third output terminals. The powersources may be DC voltages and/or AC voltages. At least one of the thirdinput terminals and/or the fourth input terminals may be connectable toa ground. The third output terminals may be connectable to at least oneof the first input terminals and the second input terminals. Thevoltages of at least one of the first input terminals and the secondinput terminals are configurable to be above or below the potential ofthe ground.

Regulating a reference voltage at one or more points in a power systemmay increase lifetime of components of the power system by alleviatingcertain voltage-affected degradation effects, for example, PotentialInduced Degradation (PID). For example, if a voltage at a DC terminal ofa PV string is regulated to be at a non-negative voltage (e.g. 0V, 10Vor 50V), the entire string may be of non-negative voltage, and PID(which may be common in systems featuring negative voltages with respectto ground) may be alleviated or reduced. Another benefit of regulating areference voltage at one or more points in a power system may be toenable extension of photovoltaic strings by referencing certain pointsin the power system to a voltage within regulatory limits.

As noted above, this Summary is merely a summary of some of the featuresdescribed herein. It is not exhaustive, and it is not to be a limitationon the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood with regard to the followingdescription, claims, and drawings. The present disclosure is illustratedby way of example, and not limited by, the accompanying figures. In thedrawings, like numerals reference similar elements.

FIG. 1A illustrates a block diagram of a power system, according toillustrative aspects of the disclosure.

FIG. 1B illustrates a block diagram of a power system, according toillustrative aspects of the disclosure.

FIG. 1C illustrates a block diagram of a power system, according toillustrative aspects of the disclosure.

FIG. 1D illustrates a block diagram of a power system, according toillustrative aspects of the disclosure.

FIG. 1E illustrates circuitry which may be found in a power device suchas power devices shown in FIG. 1A, according to illustrative aspects ofthe disclosure.

FIG. 1F illustrates a block diagram of a power system, according toillustrative aspects of the disclosure.

FIG. 2A shows a block diagram of further details of a controller,according to illustrative aspects of the disclosure.

FIG. 2B shows a flowchart of a method, according to illustrative aspectsof the disclosure.

FIG. 3A shows a power system, according to illustrative aspects of thedisclosure.

FIG. 3B shows a power system, according to illustrative aspects of thedisclosure.

FIG. 4A shows a power system, according to illustrative aspects of thedisclosure.

FIG. 4B shows a power system, according to illustrative aspects of thedisclosure.

FIG. 5 shows a power system, according to illustrative aspects of thedisclosure.

FIG. 6A shows a flowchart of a method, according to illustrative aspectsof the disclosure.

FIG. 6B shows a flowchart of a method, according to illustrative aspectsof the disclosure.

FIG. 7 shows a voltage-current graph, according to illustrative aspectsof the disclosure.

FIG. 8 shows a power system, according to illustrative aspects of thedisclosure.

DETAILED DESCRIPTION

In the following description of various illustrative features, referenceis made to the accompanying drawings, which form a part hereof, and inwhich is shown, by way of illustration, various features in whichaspects of the disclosure may be practiced. It is to be understood thatother features may be utilized and structural and functionalmodifications may be made, without departing from the scope of thepresent disclosure.

By way of introduction, features may be directed to system and methodsin an interconnected power system to enable the voltage applied toterminals of an inverter are no longer floating voltages but may insteadbe established and maintained to be above the potential of a groundand/or earth potential.

The term “multiple” as used here in the detailed description indicatesthe property of having or involving several parts, elements, or members.The claim term “a plurality of” as used herein in the claims sectionfinds support in the description with use of the term “multiple” and/orother plural forms. Other plural forms may include for example regularnouns that form their plurals by adding either the letter ‘s’ or ‘es’ sothat the plural of converter is converters or the plural of switch isswitches for example.

The terms, “substantially”, and, “about”, used herein include variationsthat are equivalent for an intended purpose or function (e.g., within apermissible variation range). Certain ranges are presented herein withnumerical values being preceded by the terms “substantially” and“about”. The terms “substantially” and “about” are used herein toprovide literal support for the exact number that it precedes, as wellas a number that is near to or approximately the number that the termprecedes. In determining whether a number is near to or approximately aspecifically recited number, the near or approximating unrequited numbermay be a number, which, in the context in which it is presented,provides the substantial equivalent of the specifically recited number.

Reference is now made to FIG. 1A, which illustrates a power system 180 aand details of wiring configurations 111 and their connections to systempower device 107, according to illustrative aspects of the disclosure.System power device 107 may be a direct current (DC) to alternatingcurrent (AC) inverter and load 109 may be a utility grid, a homeelectrical system or other load such as a single phase and/or threephase AC motor for example. System power devices 107 and system powerdevices described later may be, for example, a single phase and/or threephase DC to AC converter (also known as an inverter), a DC combiner box,and/or a monitoring, communication and/or control device. Multiplesystem power devices 107 may be connected in parallel to each other suchthat the inputs to system power devices 107 are connected in paralleland the outputs of system power devices 107 are also connected inparallel. According to some features, the inputs to system power devices107 may be connected in parallel, but the outputs of system powerdevices 107 may be connected to individual, unconnected loads. Accordingto some features, the outputs of system power devices 107 may beconnected in parallel, but the inputs of power devices 107 may beconnected to individual, unconnected power sources.

System power devices 107 may have an input at terminals designated asterminals V+ and V− and terminal V_(CP). System power device 107 mayinclude connection terminal V_(CP) which may optionally connect toanother connection terminal V_(CP) of another system power device 107.According to some features, terminal V_(CP) may be a terminal internalto system power device 107 and not accessible for direct electricalconnection to an external device (e.g., a different system power device107).

Converter 110 may be connected to power supply PSC and may provide avoltage to a terminal of system power device 107. In FIG. 1A, an outputof converter 110 is shown connected to DC terminal V− of system powerdevice 107. According to some features, the output may optionallyconnect to DC terminal V+ of system power device 107 and/or connectionterminal V_(CP). An input to converter 110 may be from power supply PSC,where one of the input connections to converter 110 is connected toground and/or earth. Power supply PSC may provide a source of DC powerto be converted by converter 110. The source of DC power may be providedfrom a power source 101 (e.g., a PV generator) connected to power device103/103 a, from a power device 103/103 a, from the string of seriesconnected power devices 103/103 a and/or from an auxiliary source of DCpower which may be separate from the DC power of power system 180 a(e.g. from a storage device such as a battery). The source of DC powermay be provided from a conversion of AC power provided from the outputof system power device 107, an AC grid supply which may or may not beconnected to system power device 107, and/or from an auxiliary source ofAC power which may be separate from the AC power of power system 180 a.According to some features, PSC may be an AC power source (e.g., aflywheel storage device or a wind turbine) and converter 110 may be anAC-to-DC converter.

Using power supply PSA as an example which may also apply to the otherpower supplies PS1-PSn, PSB, PSC and their respective converters 110,converter 110 may have a switch SA. Switch SA may be configurable toconnect or disconnect the output of converter 110 from terminals Y, V+.Similarly, switches S1-Sn may be configurable to connect or disconnectthe output of respective converters 110 from terminals X, and switchesSB/SC may be configurable to connect or disconnect the output ofrespective converters 110 from terminals Z, V−. In the drawings, aground is shown (as a solid line) with a connection to the point whereone of the terminals of power supplies PS1-PSn, PSA, PSB, PSC connectsto an input terminal of respective converter 110. Alternatively, aground (in dotted line) may connect to one of the output terminals ofrespective converter 110, and power supplies PS1-PSn, PSA, PSB, PSCconnected to the input of converters 110 may be left without a directconnection to ground. In general, switches S1-Sn, SA, SB and SC may beconnected separately to their respective converters 110 or may be anintegrated/internal part of respective converters 110. For descriptionsand drawings that follow, switches on the outputs of converters 110 arenot explicitly shown, but may or may not be included on the output ofconverters 110. Similarly, in the descriptions that follow, groundconnections on the outputs of converters 110 (not shown in thedescriptions and diagrams that follow) may be used instead ofconnections to the point where one of the terminals of power suppliesPS1-PSn, PSA, PSB, PSC connects to an input terminal of a respectiveconverter 110.

Multiple wiring configurations 111 are shown connected in parallel atterminals V+ and V− which connect to the input of system power device107 to provide voltage input V+− to the input of system power device107. The output of system power device 107 may connect to load 109. Eachwiring configuration 111 may include one or more power sources 101 whichmay be connected to a respective power device 103 and/or power device103 a at terminals W, X. The outputs of power devices 103/103 a atterminals Y, Z may be connected together to form a serial string whichconnects between terminals V+ and V−. As such, for ‘m’ strings, the ‘m’strings may provide respective currents I_(string 1)-I_(string m) intopower device 107 and voltage V+− across input terminals of power device107. Connections between power devices 103/103 a and strings of powerdevice 103/103 a devices connected to system power devices 107 may be byuse of power lines 120.

Converters 110 are shown connected to system power device 107 and mayalso be connected to power devices 103/103 a. Converter 110 may be anintegrated part of system power devices 107/power devices 103/103 aand/or retrofitted to system power devices 107/power devices 103/103 a.Multiple converters 110 within wiring configuration 111 are shown wherefor each converter 110, a number of ‘n’ power supplies PS1-PSn areconnected to the input of each respective converter 110, where one ofthe inputs to each converter 110 may be connected ground and/or earth.The output of each converter 110 with respective power supplies PS1-PSnmay be connected to terminal X of power devices 103 a/103.Alternatively, the output of each converter 110 with respective powersupplies PS1-PSn may be connected to terminal W of power devices 103a/103. Power supply PSA connected to converter 110 has the output ofconverter 110 connected to terminal Y of power device 103 a but may alsoconnect to terminal Z of power device 103 a. In a similar manner, anumber of power supplies, similar to power supply PSA, with respectiveconnections to converters 110, may have respective outputs of converters110 which connect to terminal Y and/or Z of remaining power devices 103in wiring configurations 111. According to some features describedbelow, converter 110 may be a DC to DC converter such as a Buck, Boost,Buck/Boost, Buck+Boost, Cuk, Flyback, single-ended primary-inductorconverter (SEPIC) and/or forward converter, switched auto-transformer ora charge pump. In other descriptions below converters 110 may be AC toDC converters such as uncontrolled diode rectifier circuits,phase-controlled rectifiers and/or switched mode power supply (SMPS).

Power supplies PS1-PSn, PSA may provide a source of DC power to beconverted by converters 110. The source of DC power may be provided froma power source 101 connected to power device 103/103 a, from a powerdevice 103/103 a, from the string of series connected power devices103/103 a and/or from an auxiliary source of DC power which may beseparate from the DC power of power system 180 a. The source of DC powermay be provided from a conversion of AC power provided from the outputof system power device 107, an AC grid supply which may or may not beconnected to system power device 107, and/or from an auxiliary source ofAC power which may be separate from the AC power of power system 180 a.Features and operation of converters 110 are described in greater detailbelow in the descriptions which follow.

According to some features, one or more wiring configurations 111 mightnot include power devices 103 a or 103. For example, a wiringconfiguration 111 may include multiple power sources 101 directlyconnected in series or in parallel. For example, a wiring configuration111 may have ten, twenty or thirty serially-connected photovoltaicpanels. According to some features, a wiring configuration 111 mayinclude a first group of one or more directly connected power sources101, with a second group of one or more power sources 101 connected viapower devices 103 a or 103 connected to the first group. Thisarrangement may be useful in power installations where some powersources 101 may be susceptible to factors which reduce power generation(e.g. PV generators which are occasionally shaded by shade, windturbines which occasionally suffer from a reduction in wind) and whereother power sources 101 are less susceptible to power-reducing factors.

Whereas power supplies PS1-PSn, PSA and respective converters 110 may beincluded in a wiring configuration 111, it may also be possible toconnect a power supply and a corresponding converter to an overallparallel connection of wiring configurations 111. An example of theconnection to the overall parallel connection may be power supply PSBand its respective converter 110 output is shown connected to terminalZ/V− via switch SB. In a similar way, the connection to the overallparallel connection may be power supply PSA and a correspondingconverter 110 may be connected to terminal Y/V+ via switch SA. A powersupply and corresponding converter may be electrically terminated in ajunction box and located in proximity to power sources 101/power modules103/103 a, at some point in the wiring of power cables 120 betweenwiring configurations 111 and system power devices 107, and/or at powerdevices 107 for example.

As shown in FIG. 1A, the power supplies PS1-PSn, PSA, and PSC connectedvia a converter 110 to a terminal (e.g. any of terminals X, terminal V−,or terminal V+) in wiring configuration 111 may ensure that the voltageat each terminal is maintained at a desirable voltage point with respectto the ground potential, or ensure voltages V+ and V− applied to systempower device 107 to be symmetrical at terminals V+ and V− of systempower device 107 with respect to terminal Vcp which may also beconnected to earth potential for example. With respect to FIG. 1A andother figures which follow, multiple power supplies PS1-PSn, PSA, PSB,PSC and respective converters 110/switches S1-Sn, SA, SB, SC are shownto illustrate where use of one or more power supplies and converters 110may be connected to establish that the voltage at each terminal V+, V−is maintained at a desirable voltage point with respect to the groundpotential, or to ensure that voltages applied to terminals V+ and V− ofsystem power device 107 are symmetrical at terminals V+ and V−.

Reference is now made to FIG. 1B, which illustrates a power system 180b, according to illustrative aspects of the disclosure. Two or morestrings of serially connected power sources 101 may be connected acrossthe respective inputs of system power devices 107 as DC voltages V+−aand V+−b. Power lines 120 connect power sources 101 together in seriesand the string formed thereby to the input of a system power device 107.The outputs of system power devices 107 may be connected in parallel andto load 109. Power supplies PSC1/PSC2 may provide a respective DC inputto respective converters 110. Features included and described in furtherdetail in the descriptions of converters 110 herein may allow both powersupplies PSC1/PSC2 via respective converters 110 to be connected torespective system power devices 107 or just one of power suppliesPSC1/PSC2 to be connected to a system power device 107. Connection of anoutput of converter 110 may be to either terminal (V+, V−) of systempower device 107. One of the terminals of power supplies PSC1/PSC2 maybe referenced to a desirable voltage point with respect to ground and/ora ground potential as shown.

For example, as shown in FIG. 1B, a first string of serially-connectedpower sources 101 may be connected to the input of a first system powerdevice 107, and a second string of serially-connected power sources 101may be connected to the input of a second system power device 107. Thefirst and second system power devices might not be connected at inputterminals and may be (as shown in FIG. 1B) connected in parallel at theoutput side of the system power devices 107. According to some features,power sources PSC1 and PSC2 and corresponding converters 110 may both befeatured, for example, where power sources PSC1 and PSC2 andcorresponding converters 110 are integrated in system power devices 107.According to some features (e.g., where a power source PSC1/PSC2 and acorresponding converter 110 are retrofit to a power system), a singlepower source and converter may be connected to the first system powerdevice 107, and compensation voltage output by converter 110 maypropagate to the second system power device 107 due to theparallel-output-connection of the first and second system power devices107.

A control feature of power system 180 b may be to establish and maintainthe voltage applied to a terminal V− to be above the potential of theground connection provided by a converter 110 or to establish andmaintain the voltage applied to terminal V− to be below the potential ofthe ground connection provided by converter 110 if the polarity of theinput to converter 110 from the power supply is reversed for example.Yet further, the control feature may include the feature to ensurevoltage V+− applied to system power device 107 to be symmetrical atterminals V+ and V− of system power device 107. In other words, an equalamount of positive DC voltage and negative DC voltage may be applied onrespective terminals V+ and V− of system power device 107 to maintain asymmetric string voltage across system power device 107.

Power supplies PSC1/PSC2 may provide sources of DC power to be convertedby respective converters 110. The source of DC power may be providedfrom a power source 101 connected to power device 103/103 a, from apower device 103/103 a, from the string of series connected powerdevices 103/103 a and/or from an auxiliary source of DC power which maybe separate from the DC power of power system 180 b (e.g. from a storagedevice such as a battery). The source of DC power may be provided from aconversion of AC power provided from the output of system power device107, an AC grid supply which may or may not be connected to system powerdevice 107, and/or from an auxiliary source of AC power which may beseparate from the AC power of power system 180 b. According to somefeatures, power supplies PSC1/PSC2 may be AC power sources (e.g., aflywheel storage device or a wind turbine) and converters 110 may beAC-to-DC converters.

Reference is now made to FIG. 1C, which illustrates a power system 180c, according to illustrative aspects of the disclosure. Power system 180c may be a DC-only system where the DC output of wiring configuration111, described above with respect to FIG. 1A, is connected to a DC load109. Even though one wiring configuration 111 is shown in FIG. 1C, itshould be understood that multiple wiring configurations 111 may beconnected together in various series/parallel and/or parallelinterconnections that may be applied to DC load 109. Alternatively, orin addition, power supply PSC3 may be connected to the negative (−)terminal of DC load 109 and/or the positive (+) terminal of DC load 109.One or more power supplies PSn located/connected in wiring configuration111 (e.g. at inputs to power devices 103 and/or at intermediate pointswithin wiring configuration 111) may enable voltage V+− applied to DCload 109 to be symmetrical at terminals + and − of DC load 109. In otherwords, an equal amount of positive DC voltage and negative DC voltagemay be applied on respective terminals + and − of DC load 109 tomaintain a symmetric string voltage across load 109. Load 109 may be aDC load such as a DC motor, a battery and/or be the input of a DC to DCconverter or the input of a DC to AC inverter. According to somefeatures, one or more power supplies PSn located/connected in the middleof wiring configuration 111 (e.g. at inputs to power devices 103 and/orat intermediate points within wiring configuration 111) may maintain allvoltages in wiring configuration 111 at a non-negative or non-positivevoltage with respect to ground, which may alleviate potential induceddegradation.

Reference is now made to FIG. 1D, which illustrates a power system 180d, according to illustrative aspects of the disclosure. Power system 180d includes a series string of micro inverter 107 a AC outputs connectedto an AC load 109. The outputs of micro inverter 107 a may be singlephase or three phase. The DC inputs to each of the micro inverters 107 amay be supplied by a power source 101. Multiple power supplies PS1,PS2-PSn may connect to terminals V− of respective micro inverters 107 avia the outputs of converters 110. The inputs of converters 110 mayconnect to respective power supplies PS1, PS2-PSn. The outputs of aconverter 110 may connect to either terminal V+ or V− of a microinverter107 a.

As a numerical example, the Vac voltage across a string of seriallyconnected inverters may be 110 Vrms. Power source PS1 may be connectedto a converter 110 configured to output 150 VDC to an input (asillustrated) or output of inverter 107 a, ensuring that the voltage atany point in power system 180 d does not fall below 0V with respect toground.

Reference is now made to FIG. 1E, which illustrates circuitry that maybe found in a power device 103, according to illustrative aspects of thedisclosure. Power device 103 may be similar to or the same as powerdevices 103/103 a shown in FIG. 1A which may provide respective inputand output terminals W, X and Y, Z. Input and output terminals W, X andY, Z may provide connection to power lines 120 (not shown). According tosome features, power device 103/103 a may include power circuit 135.Power circuit 135 may include a direct current-direct current (DC/DC)converter such as a Buck, Boost, Buck/Boost, Buck+Boost, Cuk, Flybackand/or forward converter, or a charge pump. In some features, powercircuit 135 may include a direct current to alternating current (DC/AC)converter (also known as an inverter), such as a micro-inverter. Powercircuit 135 may have two input terminals and two output terminals, whichmay be the same as the input terminals and output terminals of powerdevice 103/103 a. In some features, Power device 103/103 a may includeMaximum Power Point Tracking (MPPT) circuit 138, configured to extractincreased power from a power source.

According to some features, power circuit 135 may include MPPTfunctionality. In some features, MPPT circuit 138 may implementimpedance matching algorithms to extract increased power from a powersource the power device may be connected to. Power device 103/103 a mayfurther include controller 105 such as a microprocessor, Digital SignalProcessor (DSP), Application-Specific Integrated Circuit (ASIC) and/or aField Programmable Gate Array (FPGA).

Still referring to FIG. 1E, controller 105 may control and/orcommunicate with other elements of power device 103/103 a over commonbus 190. According to some features, power device 103/103 a may includecircuitry and/or sensors/sensor interfaces 125 configured to measureoperating power parameters directly or receive measured operating powerparameters from connected sensors and/or sensor interfaces 125configured to measure operating power parameters on or near the powersource, such as the voltage and/or current output by the power sourceand/or the power output by the power source. According to some features,the power source may be a photovoltaic (PV) generator comprising PVcells, and a sensor or sensor interface may directly measure or receivemeasurements of the irradiance received by the PV cells, and/or thetemperature on or near the PV generator.

Still referring to FIG. 1E, according to some features, power device103/103 a may include communication interface 129, configured totransmit and/or receive data and/or commands from other devices.Communication interface 129 may communicate using Power LineCommunication (PLC) technology, acoustic communications technology, oradditional technologies such as ZIGBEE™, Wi-Fi, BLUETOOTH™, cellularcommunication or other wireless methods. Power Line Communication (PLC)may be performed over power lines 120 between power devices 103/103 aand system power device (e.g. inverter) 107 which may include a similarcommunication interface as communication interface 129.

According to some features, power device 103/103 a may include memory123, for logging measurements taken by sensor(s)/sensor interfaces 125to store code, operational protocols or other operating information.Memory 123 may be flash, Electrically Erasable Programmable Read-OnlyMemory (EEPROM), Random Access Memory (RAM), Solid State Devices (SSD)or other types of appropriate memory devices.

Still referring to FIG. 1E, according to some features, power device103/103 a may include safety devices 160 (e.g. fuses, circuit breakersand Residual Current Detectors). Safety devices 160 may be passive oractive. For example, safety devices 160 may include one or more passivefuses disposed within power device 103/103 a where the element of thefuse may be designed to melt and disintegrate when excess current abovethe rating of the fuse flows through it, to thereby disconnect part ofpower device 103/103 a so as to avoid damage. According to somefeatures, safety devices 160 may include active disconnect switches,configured to receive commands from a controller (e.g. controller 105,or an external controller) to short-circuit and/or disconnect portionsof power device 103/103 a, or configured to short-circuit and/ordisconnect portions of power device 103/103 a in response to ameasurement measured by a sensor (e.g. a measurement measured orobtained by sensors/sensor interfaces 125). According to some features,power device 103/103 a may include auxiliary power circuit 162,configured to receive power from a power source connected to powerdevice 103/103 a, and output power suitable for operating othercircuitry components (e.g. controller 105, communication interface 129,etc.). Communication, electrical connecting and/or data-sharing betweenthe various components of power device 103/103 a may be carried out overcommon bus 190. According to some features, auxiliary power circuit 162may be connected to an output of a power device 103/103 a and designedto receive power from power sources connected to other power devices.

Power device 103/103 a may include or be operatively attached to amaximum power point tracking (MPPT) circuit. The MPPT circuit may alsobe operatively connected to controller 105 or another controller 105included in power device 103/103 a which may be designated as a primarycontroller. Power device 103 a in FIG. 1A may be an example of a powerdevice having primary controller, and in this example power devices 103are secondary devices having secondary controllers. A primary controllerin power device 103 a may communicatively control one or more otherpower devices 103 which may include controllers known as secondarycontrollers. Once a primary/secondary relationship may be established, adirection of control may be from the primary controller to the secondarycontrollers. The MPPT circuit under control of a primary and/orsecondary controller 105 may be utilized to increase power extractionfrom power sources 101 and/or to control voltage and/or current suppliedto system power device (e.g. an inverter or a load) 107. According tosome aspects of the disclosure, a primary power device 103 a might notbe featured, and wiring configuration 111 may feature power devices 103,without any of power devices 103 featuring a primary controller.

Referring still to FIG. 1E, in some features, power device 103/103 a mayinclude bypass unit Q9 coupled between the inputs of power circuit 135and/or between the outputs of power circuit 135. Bypass unit Q9 and/orpower circuit 135 may be a junction box to terminate power lines 120 orto provide a safety feature such as fuses or residual current devices.Bypass unit Q9 may also be an isolation switch for example. Bypass unitQ9 may be a passive device, for example, a diode. Bypass units Q9 may becontrolled by controller 105. If an unsafe condition is detected,controller 105 may set bypass unit Q9 to ON, short-circuiting the inputand/or output of power circuit 135. In a case in which the pair of powersources 101 are photovoltaic (PV) generators, each PV generator providesan open-circuit voltage at its output terminals. When bypass unit Q9 isON, a PV generator may be short-circuited, to provide a voltage of aboutzero to power circuit 135. In both scenarios, a safe voltage may bemaintained, and the two scenarios may be staggered to alternate betweenopen-circuiting and short-circuiting PV generators. This mode ofoperation may allow continuous power supply to system control devices,as well as provide backup mechanisms for maintaining a safe voltage(i.e., operation of bypass unit Q9 may allow continued safe operatingconditions).

In some features, a power device 103/103 a may comprise a partial groupof the elements illustrated in FIG. 1E. For example, a power device103/103 a might not include power circuit 135 (i.e. power circuit 135may be replaced by a short circuit, and a single bypass unit Q9 may befeatured. In a scenario where power circuit 135 is not present, powerdevice 103/103 a may be still used to provide safety, monitoring and/orbypass features.

Reference is now made to FIG. 1F, which illustrates a power system 180 eand details of wiring configurations 111 a-1-111 a-n connected to systempower devices 107, according to illustrative aspects of the disclosure.Wiring configuration 111 a-1 may be the same as wiring configuration 111a-n or may be different. For the sake of ease of discussion thatfollows, wiring configurations are considered the same and referred toas wiring configuration(s) 111 a-n. Power system 180 e is similar topower system 180 a of FIG. 1A in that multiple wiring configurations 111a-n are connected in parallel and provide voltage V+− to system powerdevices 107 just like multiple wiring configurations 111 are connectedin parallel to provide voltage V+ to system power devices 107 atterminals V+ and V− in FIG. 1A. Wiring configuration 111 a-n may includea series connection of power sources 104 and/or a single power source104, where the series connection is connected across terminals V+ and V−of system power devices 107. Alternatively, wiring configuration 111 a-nmay include various series/parallel connections of power sources 104.Power sources 104 may be similar and/or dissimilar, for example, powersources 104 may similarly be batteries but dissimilar in terms of thebattery type (for example Nickel-cadmium (NiCad), Lithium, lead acid),the voltages provided by each battery as well as ratings of each batteryin terms of ampere hour (Ah) for example. As such, power sources 104 maybe a variety of power sources such as batteries, photovoltaic panels, DCgenerators and/or a combination of power source 101 and respective powerdevice 103/103 a as shown with respect to power system 180 a. Accordingto features of the disclosure herein, and as shown in FIG. 1F, powerdevices 103/103 a might not be featured at all, rather, a series stringof power sources may be formed by directly serially connecting outputterminals of each power source 104.

Connections of power supplies PS1, PSA and PSC to terminals Y/V+ and/orZ/V−via converters 110, according to descriptions which follow, mayprovide the option of the voltage applied to terminals V− and V+ to beno longer floating. Instead the voltages on terminals V− and V+ may beestablished above the potential of the ground by virtue of groundconnections which may be provided by converters 110. As such by way ofnon-limiting example, if power sources 104 are photovoltaic panels,during daytime operation terminals V− and V+ may be kept above groundpotential and at night below ground potential or vice versa. Such anarrangement for nighttime and/or daytime operation may mitigate voltageinduced power degeneration of the photovoltaic panels during daytimeoperation as well as to affect a repair to the photovoltaic panels atnighttime. Alternatively, or in addition, to mitigate voltage inducedpower degeneration of the photovoltaic panels for daytime operation, forone day during daytime operation terminals V− and V+ may be kept aboveground potential and the next day below ground potential and so on, inan alternating fashion.

According to features of the disclosure herein, a converter 110 may beconfigured to output a first voltage during the daytime and a secondvoltage at night. As a non-limiting example, a converter 110 may beintegrated into a system power device 107 and may be configured tooutput a voltage to set the voltage operating point at terminal V−. Whensubstantial input power (e.g., a power level above a first threshold) ismeasured at the system power device 107 (indicating a daytime conditionof substantial production of photovoltaic power), converter 110 mayoutput, for example, 10V, to ensure that all photovoltaic generatorsconnected to the system power device input are referenced to a positivevoltage. When an insubstantial input power (e.g., a power level underthe first threshold or under a second threshold) is measured at thesystem power device 107 (indicating a nighttime condition of lack ofsubstantial production of photovoltaic power), converter 110 may output,for example, 100V, to increase the positive voltage bias of terminal V−.Increasing the positive voltage bias of connected PV generators (e.g.,by increasing the positive voltage bias of terminal V−) may reversepotential-induced degradation effects that may develop on PV generatorsduring the daytime.

A single power supply connected via a converter 110 to a reference point(e.g. any of terminals X indicated in FIG. 1A, or terminal V−, orterminal V+) in wiring configuration 111 may be sufficient to referencethe voltage of wiring configuration 111 to a desirable voltage pointand/or ground potential. Multiple power sources PS1 . . . PSnillustrated show various possibilities for implementation and not toindicate that all of the power sources and corresponding converters 110are required. In descriptions above and those that follow for powersystems, power sources (power sources PS1 . . . PSn for example) may bereferenced to a desirable voltage point with respect to ground and/orground potential.

Reference is now made to FIG. 2A which shows a block diagram of furtherdetails of control unit 20 which includes a controller 200, according toillustrative aspects of the disclosure. Controller 200 may include amicroprocessor, microcontroller and/or digital signal processor (DSP)which may connect to a memory 210. With respect to FIG. 1A, controller200 in one converter 110 may serve as a primary controller to the othercontrollers 200 of the other converters 110. As such, communicationsinterface 202 connected to controller 200 may provide communicationsbetween controllers 200 and other controllers 200/105 included in powersystem 180 a for example. Alternatively, a converter 110 if located inproximity to power devices 103/103 a and/or system power devices 107 maybe controlled by a controller of power devices 103/103 a and/or systempower devices 107 but may still retain the other features included incontroller 200.

The communications to and from communications interfaces 202 ofconverters 110 may be by power line communication (PLC) over power lines120. Communications in communications interface 202 may also includemeasured or sensed communication parameters via sensors 204 a/sensorinterface 204. Communications interfaces 202 may communicate with alocal area network or cellular network in order to establish an internetconnection which for example may provide a feature of remote control,remote monitoring and/or reconfiguration of power devices 103/103 aand/or system power device 107 for example. Controller 200 may furtherinclude auxiliary power circuit 262, configured to receive power from apower source connected to power device 103/103 a, system power device107 and output power suitable for operating other circuitry components(e.g. controller 200, communication interface 202, etc.). According tosome features, auxiliary power circuit 262 may be connected to an outputof a power device 103/103 a, system power device 107, power suppliesPS1-PSn, PSA, Ps4 and designed to receive power from power sourcesconnected to other power devices and/or sources of power independentfrom power produced by power system 180 a.

In the descriptions that follow, example method of design and operationfor converter 110 are shown where power supplied to the input ofconverter 110 is an AC power and/or a DC power which may be supplied forexample from a power source 101 connected to power device 103/103 a,from a power device 103/103 a, from the string of series connected powerdevices 103/103 a and/or from an auxiliary source of DC power which maybe separate from the DC power of a power system 180 a.

Reference is now made to FIG. 2B which shows a flowchart of a method 201according to illustrative aspects of the disclosure. Method 201 may beapplied to power system 180 a of FIG. 1A in the description thatfollows. Steps of method 201 may be implemented by one of thecontrollers of system power devices 107, power devices 103/103 a and/orconverters 110 acting as a primary controller. At step 203, DC powerfrom wiring configurations 111 may be provided and applied to the inputof system power devices 107 (e.g., inverters) across terminals V+ andV−. Within a wiring configuration 111, DC power may be provided via astring of serially connected power device 103/103 a outputs where theinputs to each of the power devices 103/103 a is connected to a powersource 101. Alternatively, in a wiring configuration 111, a string ofinterconnected (e.g., connected in series or in parallel) power sources101 may be applied to the inputs of system power devices 107.

At step 205, DC power (power=voltage×current) from the parallelconnected wiring configurations 111 may be inverted by system powerdevices 107 to an AC power (power=voltage×current) output that may beapplied to load 109.

At step 207, electrical parameters (e.g. voltage, current, power,resistance) may be sensed on terminals V−, V_(CP) and/or V+ by a sensorof system power device 107. At about the same time, sensors/sensorinterfaces 125 of power device 103/103 a and/or the sensor interface204/sensors 204 a of converters 110 may sense electrical parameters onterminals W, X, Y, Z, V− and V+.

By way of non-limiting example, operation of power supply PS1 isreferred to where power system 180 a has one wiring configuration 111,where the input of converter 110 is connected to power supply PS1, andwhere all other power supplies and converters are not referred to orused for ease of discussion. At about the same time of step 207, in step209, the source of DC voltage from power supply PS1 may be converted byconverter 110 to provide a greater voltage at the output of converter110 responsive to the electrical parameters sensed on W, X, Y, Z, V− andV+ in step 207. In other words, converter 110 is functioning as a boostconverter. The level of the greater voltage produced at the output ofconverter 110 may be responsive to the electrical parameter sensed instep 207 or may be produced independently of the electrical parameterssensed in step 207. As such, responsive to the electrical parametersensed, for example voltage of terminals Z and/or V− (but may includealso terminals V+ and V_(CP)), the application of the output ofconverter 110 to terminal X and/or Z at step 211 may add the boostedoutput voltage of converter 110 to terminal V− of system power device107. As such, in step 213, the voltage applied to terminal V− is nolonger floating but is established above the potential of the groundconnection provided by converter 110.

Included in step 213 by operation of the other steps of method 201 ismaintenance of the voltage applied to terminal V− above the potential ofthe ground connection provided by converter 110. Moreover, if powersupply PSA is used instead of power supply PS1, and if the polarity ofpower supply PSA is reversed, the output of converter 110 connected toPSA may be applied to terminals W, Y/V+ such that the steps of method201 may establish and maintain the voltage applied to terminal V+ to bebelow the potential of the ground connection provided by converter 110.This may be desirable, for example, when power sources 101 arephotovoltaic panels having properties where potential induceddegradation (PID) may be reduced by maintaining all of the photovoltaicpanels at a voltage below zero with respect to ground. Further, whenapplying the steps of method 201 in wiring configuration 111, it may bepossible to make use of a power supplies PSn located/connected in themiddle of wiring configuration to enable voltage V+− applied to systempower devices to be symmetrical at terminals V+ and V−. In other words,an equal amount of positive DC voltage and negative DC voltage may beapplied on respective terminals V+ and V− of system power device 107 tomaintain a symmetric string voltage.

By way of another non-limiting example, operation of power supply PSB isreferred to where power system 180 a has multiple wiring configuration111, where the input of converter 110 is connected to power supply PSBand, for ease of discussion, all other power supplies and converters arenot referred to or used. At about the same time of step 207, at step209, the source of DC voltage from power supply PSB may be converted byconverter 110 to provide an output voltage that is greater than thevoltage at the input of converter 110 responsive to the electricalparameters sensed in step 207. In other words, converter 110 isfunctioning as a boost converter for all of the wiring configurations111. The level of the voltage produced at the output of converter 110may be responsive to the electrical parameter sensed in step 207 or maybe produced independently of the electrical parameters sensed in step207. As such, responsive to the electrical parameter sensed, for examplevoltage of terminals Z and/or V− but may include also terminals V+ andV_(CP), the application of the output of converter 110 to terminal Zand/or V− at step 211 may add the boosted output voltage of converter110 to terminal V− of system power device 107.

By way of non-limiting numerical example, assume that a desirablevoltage on terminal V+ is 510 volts (v) and the voltage on terminal V−is substantially above ground potential (zero volts), +10 v for example.A controller of power device 107 and/or power modules 103/103 a may beutilized to maintain a string voltage for each wiring configuration 111of 500 v (510 v−10 v). The string voltage of 500 v may be a floatingvoltage but any one of power sources PS1-PSn, PSA, PSB or PSC andrespective converter 110 may be used (switches S1-Sn, SA, SB, SC used toselect which power supply converter 110 for example) to set the voltageon terminal V− to be +10 volts and 510 v on terminal V+. As such sensorssensors/sensor interfaces 125/204/204 a may be used to sense the voltageat terminals Y/V+ and Z/V− (step 207). Converter 110 may be used toapply a positive voltage (with respect to ground to terminal) toterminal Z/V− (step 211) via conversion of power from power supply PSB(step 209) so that terminals Y/V+ and Z/V− are above earth potential. Assuch, if the voltage sensed on terminal Y/V+ is +250 v and the voltagesensed on terminal Z/V− is −250, so that the differential voltage is 500v, the output of the boost converter may add 260 v to terminal Z/V− sothat by Kirchhoff voltage law the voltage on terminal Z/V− is 260 v−250v=10 v and the voltage on terminal Y/V+ is 510 v=260 v+250 v.

As such, in step 213, the voltage applied to terminal V− is no longerfloating but is established above the potential of the ground connectionprovided by converter 110 for all wiring configurations 111. Included instep 213 by operation of the other steps of method 201 is maintenance ofthe voltage applied to terminal V− above the potential of the groundconnection provided by converter 110. Moreover, if power supply PSB isused at the top of the wiring configurations 111 and converter 110connects to terminals Y and/or W, if the polarity of power supply PSB isreversed, the output of converter 110 connected to power supply PSB maybe applied to terminals W, Y/V+ such that the steps of method 201 mayestablish and maintain the voltage applied to terminal V+ to be belowthe potential of the ground connection provided by converter 110.

Further considerations may also be considered in an application to powersystem 180 a by use of power supply PSC instead of or in addition topower supply PSB. The overall application may use power supply PSC insteps similar to those described with respect to use of power supply PSBto again establish and maintain the voltage applied to terminal V+ to bebelow the potential of the ground connection provided by converter 110or to establish and maintain the voltage applied to terminal V+ to beabove the potential of the ground connection provided by converter 110.In a similar way, use of power supply PSC may establish and maintain thevoltage applied to terminal V− to be below the potential of the groundconnection provided by converter 110 or to establish and maintain thevoltage applied to terminal V− to be above the potential of the groundconnection provided by converter 110. The source of DC power convertedby converter 110 may be provided from a conversion of AC power providedfrom the output of system power devices 107, an AC grid supply which mayor may not be connected to system power devices 107, and/or from anauxiliary source of AC power which may be separate from the AC power ofpower system 180 a.

Reference is now made to FIG. 3A which shows a power system 180 f,according to illustrative aspects of the disclosure. Power system 180 fmay be considered to be a simplified version of power system 180 adescribed above and may be referenced as such, for the ease ofdiscussion in the description which follows. A power source 101 may beconnected to the input of power device 103/103 a at terminals W and X.Power source 101 may be a photovoltaic panel, DC generator and/orbattery/storage device. For example, power source 101 may be a string ofserially connected PV power sources, or a plurality orparallel-connected strings of PV power sources. As such, since powersource 101 is shown as not being grounded, the voltage input to powerdevice 103/103 a at terminals Y and Z may be considered a floatingvoltage. The output voltage (V+−) of power device 103/103 a at terminalsW and X may also be considered to be a floating output voltage that maybe applied to a system power device 107 at terminals V+ and V−.

A partial view of the components of the input of system power device 107is shown. System power device 107 may provide a further input terminalV_(CP) which may be the midpoint connection in the series connection oftwo input capacitors C+, C−. The series connection of two inputcapacitors C+, C− may be, for example, an input of a multi-levelinverter topology implementation of system power device 107. However,input terminal V_(CP) might not necessarily be externally provided,since according to some implementations of system power device 107, asingle capacitor connected across terminals V+ and V− along with aswitched bridge topology (not shown) included, may provide the invertertopology for system power device 107. According to some features, morethan two capacitors may be disposed between terminals V+ and V−. Forexample, 6 capacitors may be disposed between terminals V+ and V−,creating 5 midpoint voltage levels. Load 109 may be connected to theoutput of system power device 107. Load 109 may be an AC motor, atransformer, a localized grid and/or a utility grid for example.

The output of converter 110 a may be connected to terminal V−, theoutput of converter 110 a may be the same as or similar to as discussedpreviously above with respect to converter 110 and may be similarlyconnected to terminals V_(CP), V+, W and/or X. Converter 110 a is shownin FIG. 3A as a boost converter such that the input DC voltage frompower supply PS1 a is converted to an increased value of output voltageat the output of converter 110 a. Power supply PS1 a connects across theinput terminals of converter 110 a. Power supply PS1 a is a source of DCvoltage that may be provided from a power source 101 connected to powerdevice 103/103 a, from a power device 103/103 a, from a string of seriesconnected power devices 103/103 a and/or from an auxiliary source of DCpower (from auxiliary power circuit 162/262 for example) which may beseparate from the DC power of power system 180 a. Power supply PS1 a maybe same as any one of the power supplies PS1 to PSn. The converter 110 amay be same as any one of the converters 110 connected to PS1-PSn.

A first input terminal of converter 110 a connects to a ground and/orearth. A second input terminal of converter 110 a connects to a firstend of inductor L1. A second end of inductor L1 connects to the anode ofdiode D1 and a first end of switch Q1. The cathode of D1 connects to afirst end of capacitor C1. A second end of switch Q1 and a second end ofcapacitor C1 connect to the ground and/or earth. The cathode of D1 alsoconnects to a first end of resistor R1. A second end of resistor R1connects to the anode of diode D2. The cathode of diode D2 connects to afirst end of switch Q2. A second end of switch Q2 connects to terminalsZ and V− but may also alternatively be connected to V_(CP), V+, W and/orX. Switch Q2 may be an example of switches S1-Sn, SA, SB and SCdescribed above. An appropriate pulse width modulation signal or othercontrol signal may be applied to the gate (g) of switch Q1 to providethe boost function of converter 110 a such that the input DC voltagefrom power supply PS1 a is converted to an increased value of outputvoltage at the output of converter 110 a.

Reference is now made again to method 201 of FIG. 2B as applied to powersystem 180 f of FIG. 3A, according to illustrative aspects of thedisclosure. Steps of method 201 may be implemented by one of thecontrollers of system power device 107, power device 103/103 a and/orconverter 110 a. Power system 180 f uses one converter and one powersupply, and one converter and one power supply may be used with respectto power systems 180 a-180 e described above and other powers systemsdescribed below. At step 203, DC power from power source 101 may beprovided and applied to the input of system power device 107 via powerdevice 103/103 a or power source 101 may be provided and applied to theinput of system power device 107 directly (e.g., where power device103/103 a is not featured). At step 205, DC power(power=voltage×current) from power source 101 directly and/or from powerdevice 103/103 a connected to power source 101 may be inverted by systempower device 107 to an AC power (power=voltage×current) output that maybe applied to load 109. At step 207, an electrical parameter (e.g.,voltage, current, power, resistance) may be sensed on terminal V− by asensor of system device 107, sensors/sensor interfaces 125 of powerdevice 103/103 a on terminal Z and/or sensor interface 204/sensors 204a.

At about the same time of step 207, in step 209, the source of DCvoltage from power supply PS1 a may be converted by converter 110 a toprovide a greater voltage at the output of converter 110 a which isresponsive to the electrical parameter sensed in step 207. As such,responsive to the electrical parameter sensed, control of the switchingof switch Q1 may be application of an appropriate pulse width modulationsignal to the gate (g) of switch Q1. At step 211, the operation ofswitch Q2 to be ‘ON’ may add the boosted output voltage of converter 110a to terminal V− of system power device 107. As such, in step 213, thevoltage applied to terminal V− is no longer floating but is establishedabove the potential of the ground connection provided by converter 110a. Included in step 213 by operation of the other steps of method 201 iscontinuous maintenance of the voltage applied to terminal V− above thepotential of the ground connection provided by converter 110 a.

Where multiple system power devices are connected in parallel as shownwith respect to power system 180 a, diode D2 and resistor R1 may beutilized as a current limiting device and/or other current limitingcircuit to limit circulating currents between converters 110 a.Moreover, if the polarity of power supply PS1 a is reversed, the outputof converter 110 a may be applied to terminal V+ such that the steps ofmethod 201 may establish and maintain the voltage applied to terminal V+to be below the potential of the ground connection provided by converter110 a. Where multiple system power devices are connected in parallel asshown with respect to power system 180 a, a single converter 110 a mayprovide the reference voltage to a single system power device, and byvirtue of the parallel connection of system power devices 107, each ofthe parallel-connected power devices 107 may be referenced to thevoltage output by converter 110 a.

According to features of the disclosure, a power converter 110 a may beintegrated into a system power device 107. Where a power converter 110 ais integrated into each of multiple parallel-connected system powerdevices 107, each power converter 110 a may be synchronized to output acommon reference voltage (e.g., by a single system power device beingdesignated as a primary system device and the primary system powerdevice outputting a reference voltage to be used by the other systempower devices), or only a single integrated power converter 110 a may beconfigured to output a reference voltage, and the other integrated powerconverters 110 a may be disabled and/or might not output a referencevoltage.

Reference is now made to FIG. 3B which shows a power system 180 g,according to illustrative aspects of the disclosure. Power system 180 gis similar to power system 180 f except that power source 101 and powerdevice 103/103 a in power system 180 f may be included in power source104 of power system 180 g. Power source 104 may be as describedpreviously with respect to FIG. 1F so that power source 104 may be avariety of power sources such as a battery or batteries, photovoltaicpanel(s), DC generator(s) and/or a combination of power source 101 andrespective power device 103/103 a as shown with respect to power system180 a.

In the description above with respect to step 207 electrical parameters(e.g. voltage, current, power, resistance) may be sensed on terminalsV−, V_(CP) and/or V+ by a sensor of system power device 107, bysensors/sensor interfaces 125 of power device 103/103 a and/or thesensor interface 204/sensors 204 a of converters 110 on terminals W, X,Y, Z, V− and V+. Alternatively, or in addition, electrical parameters(e.g. voltage, current, power, resistance) may be sensed on the AC sideof system power device(s) 107 on at least one of the phases of theoutput of system power device(s) 107 and/or the neutral of system powerdevice(s) 107. As such, where the output of system power device(s) 107is 3 phase, the average voltage of the three phases may be measured(e.g. by direct measurement, or by calculation) and used in step 213, toensure that the voltage applied to terminal V− is no longer floating butis established above the potential of the ground connection provided byconverters 110/110 a. Included in step 213 by operation of the othersteps of method 201 may be continuous maintenance of the voltage appliedto terminal V− referenced to a desirable voltage point with respect toground and/or above the potential of the ground connection provided byconverters 111/110 a.

Reference is now made to FIG. 4A which shows a power system 180 h,according to illustrative aspects of the disclosure. Power source 104connects to the input of inverter 400. As discussed previously above,power source 104 may be one or more of a variety of power sources suchas batteries, photovoltaic panels, DC generators and/or a combination ofpower source 101 and respective power device 103/103 a as shown withrespect to power system 180 a. The DC voltage of power source 104connects to terminals V+ and V− of system power device 107 which mayinclude control unit 20, described above where sensors 204 a/sensorinterface 204 may be utilized to sense the electrical parameter onterminals V+, V− and on ‘n’ connection terminals V_(CP1)-V_(CPn). Theelectrical parameter may include voltage (V), current (I) and power(V×I). The ‘n’ connection terminals may be the midpoint connection inthe series connection of input capacitors C. The series connection ofmultiple input capacitors C may be an input of a multi-level invertertopology implementation of inverter 400 for example. However, inputterminals to inverter 400 on system power device 107 may provide asingle capacitor C connected across terminals V+ and V− along with aswitched bridge topology (not shown) included, which may also providethe inverter topology for inverter 400. According to some features, morethan two capacitors C may be disposed between terminals V+ and V−. Forexample, six capacitors may be disposed between terminals V+ and V−,creating five midpoint voltage levels in addition to the end voltagelevels of V+ and V−. One or more of the five midpoint voltage levels andthe two-end voltage levels may be measured to provide a referencemeasurement for regulation and control of a voltage level at one of themidpoint voltage and/or one of the end voltage levels.

Load 109 may be connected to the output of system power device 107. Load109 may be an AC motor, a transformer, a localized grid and/or a utilitygrid for example. The output of inverter 400 is shown as a single-phaseoutput but may also be a multiple phase output such as a three-phaseoutput for example. The output of inverter 400 is connected to the inputof rectifier unit 40. Rectifier unit 40 may be AC to DC converters suchas uncontrolled diode rectifier circuits, phase-controlled rectifiersand/or switched mode power supplies (SMPS). Rectifier 40 may alsoinclude a transformer which may be used to galvanically isolate betweenthe AC output of inverter 400/load 109 and the DC input of converter 110b. The transformer may also either increase and/or decrease the AC inputto rectifier unit 40.

The DC output of rectifier unit 40 connects across the input ofconverter 110 b. Converter 110 b is shown as a buck converter circuittopology. As such since one function of a buck converter may be toreduce the voltage at its input to a lower voltage at its output, atransformer may not be required in rectifier unit 40. Capacitor C3connects across the input of converter 110 b. One input terminals ofconverter 110 b connects to ground and/earth. The other input terminalof converter 110 b connects to one end of switch Q3, the other end ofswitch Q3 connects to inductor L2 and one end of switch Q4. The otherend of inductor L2 provides the output of converter 110 b and alsoconnects to one end of capacitor C4. The remaining ends of capacitor C4and switch Q4 connect to ground and/earth. The output of converter 110 bis shown connected to terminal V− but may also connect to terminal V+and/or connection terminals V_(CP1)-V_(CPn). The utilization of method201 for inverter 400 may be to establish and maintain the voltageapplied to terminal V− to be above the potential of the groundconnection provided by converter 110 b or establish and maintain thevoltage applied to terminal V− to be below the potential of the groundconnection provided by converter 110 b if the polarity of the input toconverter 110 b is reversed for example. In a similar way, inverter 400may be configured and controlled to establish and maintain the voltageapplied to terminal V+ to be above the potential of the groundconnection provided by converter 110 b or to establish and maintain thevoltage applied to terminal V+ to be below the potential of the groundconnection provided by converter 110 b, if the polarity of the input toconverter 110 b is reversed for example.

Reference is now made to FIG. 4B, which shows a power system 180 i,according to illustrative aspects of the disclosure. Power system 180 iis similar to power system 180 h but may include multiple inverters 400,each having one or more with multiple inputs from one or more powersources 104 and the output of each inverter 400 connected across a load109. Further detail of system power device 107 may include control unit20 and may also include switches DSL and DSN that may disconnect orreconnect respectively the live and neutral outputs of system powerdevice 107 from a load 109. The output of system power device 107 isshown as a single-phase output but may also be a three-phase output. Thethree-phase output may include at least three switches that maydisconnect or reconnect respectively the three live and/or neutraloutputs of system power device 107 from load 109. If power sources 104are photovoltaic generators, switches DSL and DSN may disconnect thelive and neutral outputs of system power device 107 from load 109 duringnighttime operation of power system 180 i. Switches DSL and DSN mayreconnect the live and neutral outputs of system power device 107 toload 109 during daytime operation of power system 180 i.

Reference is now made again method 201 and to power system 180 i whenpower sources 104 are photovoltaic generators and load 109 is a utilitygrid. Control units 20 of each inverter 400 may communicate with eachother where one control unit 20 may be a primary control unit and othercontrol units 20 are secondary control units. Sensors 204 a/sensorinterface 204 may be utilized to sense electrical parameters on the liveand neutral outputs of system power device 107, terminals V−,V_(CP1)-V_(CPn) and V+.

During daytime operation switches DSL and DSN may connect the live andneutral outputs of system power device 107 to load 109. At step 203, DCpowers from power sources 104 may be provided and applied to the inputsof system power devices 107.

At step 205, DC power (power=voltage×current) from power sources 104 maybe inverted by respective system power devices 107 to an AC power(power=voltage×current) output that may be applied to load 109.

At step 207, electrical parameters (e.g., voltage, current, power,resistance) may be sensed for each inverter 400 on the respectiveterminals of each system device 107 by each of the sensor interfaces204/sensors 204 a provided by each control unit 20.

At about the same time of step 207, in step 209, during daytimeoperation, the source of DC voltage from each rectifier unit 40 may beconverted by converter 110 b to provide voltages at the outputs of eachconverter 110 b that is responsive to the electrical parameters sensedin step 207 for each inverter 400. By way of non-limiting example, oneof terminals V_(CP1)-V_(CPn) may be chosen as the terminal at which thevoltage may be sensed for each inverter. As such, if the input to eachsystem power device 107 has a six-capacitor input, terminal V_(CP3) (themidpoint of the input to each system power device 107) of each inverter400 may be sensed at step 207 and an appropriate control signal sent toeach converter 110 b and/or also to power device 103/103 a that may beincluded in power source 104 from the primary control unit 20 so thateach terminal V_(CP3) is controlled and maintained (step 213) to havethe same desired voltage and terminal V− is no longer floating but isestablished above the potential of the ground connection provided byeach converter 110 b. Included in step 213 by operation of the othersteps of method 201 may be continuous maintenance of the voltage appliedto terminal V− above the potential of the ground connection provided byconverter 110 b.

By way of non-limiting numerical example, assume that a desirablevoltage on terminals V+ is 510 volts (v) and the voltage on terminal V−is substantially above ground (or a “virtual ground”) potential (zerovolts), +10 v for example. Control unit 20 may be utilized to maintainvoltage V+−for each power source 104 of 500 v (510 v−10 v) at step 205for each inverter 400. Voltage V+− of 500 v is a floating voltage (e.g.,voltage V+ might not be directly referenced to ground, rather voltage V+may be referenced to a “virtual ground”, with the “virtual ground”controlled to be at the same voltage as earth but galvanically isolatedfrom earth) but any one of rectifier units 40 and respective converter110 b may be used to set the voltage on terminal V− to be +10 volts and510 v on terminal V+ by sensing the inverting of each system powerdevice 107 (step 207). Converter 110 b for each inverter 400 may be used(step 209) to apply a respective positive voltage (with respect toground to terminal) to each terminal V− (step 211) via conversion ofpower from each rectifier unit 40 (step 209) so that each of terminalsV_(CP3) may be established and maintained (step 213) at 260 volts. Assuch, during operation each of the inverters 400, each inverter 400 mayhave different sensed parameter values needing adjustment from arespective converter 110 b to establish and maintain that terminalV_(CP3) of each inverter 400 may be established and maintained (step213) at the same value (260 volts). For example, for one converter 400,if the voltage on terminal V+ is +250 v and the voltage on terminal V−is −250 v, so that the differential voltage between terminals V− and V+is 500 v, the output of converter 110 b may add 260 v to terminal V− sothat by Kirchhoff voltage law the voltage on terminal V− is 260 v−250v=10 v and the voltage on terminal V+ is 510 v=250 v+260 v.

According to features of the disclosure, each system power device 107may be controlled to maintain an internal voltage level at asubstantially common level. For example, system power devices 107 asshown in FIG. 4B may feature a plurality of input capacitors C, creatinga plurality of intermediate voltage levels. One of the intermediatevoltage levels may be regulated (e.g. measured at step 207 of method 201when applied to system power devices 107) to be at a certain voltagelevel, with the certain voltage level regulated at each system powerdevice 107 substantially the same for all system-connected powerdevices. This regulation may be useful, for example, to prevent circularcurrent flows between system power devices 107 connected in parallel atinput terminal and/or at output terminals. The intermediate voltagepoint regulated may be an intermediate input voltage (e.g., the voltageVcp of FIG. 3A) or an intermediate output voltage (e.g., a “virtualneutral” voltage internally created but not output by system powerdevice 107 of FIG. 4B, or, where system power device 107 is designed tooutput a neutral voltage line, the neutral voltage line may be regulatedfor each system power device 107 to be at a substantially common voltagelevel).

Reference is now made to FIG. 5, which shows a power system 180 j,according to illustrative aspects of the disclosure. Converter 110includes circuitry 500 configured to regulate the output of converter110. Circuitry 500 may include one or more sensors, for example, currentand/or voltage sensors. According to the illustrative circuitry shown inFIG. 5, circuitry 500 includes two resistors RS3, RS4 connected inseries between terminal Vcpn and ground and/or earth. A first end ofresistor RS4 is connected to terminal Vcpn and a second end of resistorRS4 is connected to a first end of resistor RS3. The second end ofresistor RS3 is connected to the ground and/or earth potential.Circuitry 500 also includes a voltage sensor 502. A first end of voltagesensor 502 is connected to the first end of resistor RS3 and a secondend of voltage sensor 502 is connected to the ground and/or earthpotential. Voltage sensor 502 may also be operatively connected tocontrol unit 20 and/or controller 200. In some examples, voltage sensor502 may be part of control unit 20. In some examples, control unit 20may be located in system power device 107 and/or converter 110. Asanother example, control unit 20 may be a separate unit. Circuitry 500also includes a current sensor 504 connected in parallel to resistor R1of converter 101. Current sensor 504 is also operatively connected tocontrol unit 20 and/or controller 200. In some examples, current sensor504 may derive the current flowing through resistor R1 based on thevoltage across resistor R1 and the resistance of resistor R1(current=voltage÷resistance). In some examples, current sensor 504 maybe connected in series with resistor R1 and measure the current flowingthrough resistor R1 directly.

Circuitry 500 is configured to control the output of converter 110. Asmentioned above, in some examples, switch Q1 and/or switch Q2 may becontrolled by control unit 20. The control of these switches Q1, Q2 maybe based on one or more parameter sensed by the circuitry 500. As anexample, the one or more parameter may include: voltage, current, etc.By adjusting control of switches Q1 and/or Q2, control unit 20 mayadjust the output of converter 110. For example, increasing a duty cycleof switch Q1 may increase the voltage output by converter 110.

In cases where power system 180 j includes a plurality of system powerdevices 107, it may occur that a voltage at terminal Vcpn for one ormore of the system power devices 107 may be greater (e.g., substantiallygreater) than a target voltage that corresponds to a voltage or a targetvoltage at terminal Vcpn at one or more other system power devices 107.For example, substantially greater in this context may be within acertain range, e.g., +/−five volts, +/−tens of millivolts, +/−hundredsof millivolts, etc. If the voltage Vcpn is higher at a first systempower device than at a second system power device, then the secondsystem power device may be adversely affected, for example, shut down.In such cases, in the absence of circuitry that senses current andregulates the voltage accordingly, then other power devices 107 (e.g.,the second system power device which may be operating at or below thedesired voltage) may be inadvertently bypassed or deactivated, and onlythe one or more system power device 107 operating at a voltage greaterthan the desired voltage may continue to supply power to the load 109.In order to help allay such a scenario, the circuitry 500, in additionto sensing voltage, may also sense current, e.g., the current flowingthrough the converter 110 at resistor R1. If one or more sensedparameter is indicative of a voltage that is higher than a desiredvoltage or higher than a voltage operating point of other system powerdevices 107, then controller 200 may operate in order to decrease thevoltage output by the converter 110, which decreases the voltage atterminal Vcpn for that system power device 107.

It will be appreciated that in some examples, a converter 110, which isconnected to ground potential, and circuitry 500 may be used to regulatea similar voltage value at a plurality of terminals Vcpn for a pluralityof system power devices 107 by regulating and/or directly controllingthe voltage at terminal V−, V+, etc. In some cases, for example whereterminal Vcpn is a common neutral (or “virtual neutral”, i.e., aterminal corresponding to terminals at other system power devices 107having a similar or identical voltage without directly connecting theVcpn terminals of the various system power devices 107) for theplurality of system power devices 107, then a single circuit (e.g.circuitry 500) may be used to control the voltage at terminal Vcpn forthe plurality of system power devices 107. In some examples, forexample, where the power system has a plurality of power supplies PSnand a plurality of system power devices 107 share a common neutral or acommon “virtual neutral”, in some cases where one or more of the powersupplies PSn cease to operate, then the power system may continue tofunction with one or more of the remaining power supplies PSn providingthe required voltage to terminal V−, V+, etc.

Reference is now made to FIG. 6A which shows a flowchart of a method 601according to illustrative aspects of the disclosure. For example, method601 may be applied to power system 180 j of FIG. 5 in the descriptionthat follows. As an example, steps of method 601 may be implemented bycontrollers of system power devices 107, controllers of power devices103/103 a, and/or converters 110 acting as a primary controller.

At step 603, a current is determined and a voltage is determined.

For example, at step 603, a current related to the voltage at terminalVcpn of system power device 107 may be determined, e.g., measured bycurrent sensor 504. As an example, the current flowing through resistorR1 may be measured. In other examples, a different current may bemeasured or determined, for example, the current through diode D1, thecurrent through diode D2, the current through switch Q2, etc. In someexamples, the current may be estimated (e.g., by measuring currentthrough inductor L1 and estimating the current through resistor R1 basedon the measured current through inductor L1 and the duty cycle of switchQ1).

For example, at step 603, a voltage related to the voltage at terminalVcpn of system power device 107 may be determined, e.g., measured byvoltage sensor 502. As an example, the voltage of resistor RS3 may bemeasured. The voltage of resistor RS3 is related to the voltage atterminal Vcpn. In some cases the voltage of resistor RS3 that ismeasured may be used to derive the voltage at terminal Vcpn. In otherexamples, a different voltage may be sensed, for example, the voltage atterminal V+, the voltage at terminal V−, etc.

At step 605, a value is calculated based on the determined current andthe determined voltage. For example the value may be calculated using afunction that depends both on the current and the voltage, e.g., alinear function, a polynomial function, etc.

At step 607 the calculated value is compared to a reference value. Forexample, if the value calculated at step 605 is a voltage value then thereference value may be a reference voltage value. As an example, thereference value may be a desired voltage value, desired current value,etc.

If at step 607 it is determined that the calculated value issubstantially less than the reference value, then at step 609 thevoltage output may be increased. For example, the control unit 20, e.g.,controller 200, may control the converter 110, e.g., switch Q1 and/orswitch Q2, to increase the output voltage of the converter 110 that isoutput to terminal V−. This may control an increase in voltage atterminal Vcpn.

If at step 607 it is determined that the calculated value issubstantially equal to the reference value, or within a permissiblerange of variation from the reference value, then at step 611 thevoltage output may be substantially maintained. For example, the controlunit 20, e.g., controller 200, may control the converter 110, e.g.,switch Q1 and/or switch Q2, to substantially maintain (e.g., allowing apermissible variation, but without a substantial change in averagevoltage) the output voltage of the converter 110 that is output toterminal V−. This may maintain the voltage at terminal Vcpn.

If at step 607 it is determined that the calculated value issubstantially greater than the reference value, then at step 613 thevoltage output may be decreased. For example, the control unit 20, e.g.,controller 200, may control the converter 110, e.g., switch Q1 and/orswitch Q2, to decrease the voltage of the converter 110 that is outputto terminal V−. This may control a decrease in voltage at terminal Vcpn.

According to features of the disclosure herein, the value calculated atstep 605 may be inversely proportional or directly proportional to thedesirable change in output voltage. In the example shown in FIG. 6A, thevalue being substantially less than the reference value causes anadjustment to increase voltage output. In another example, the value maybe calculated such that the value being substantially less than areference value causes an adjustment to decrease voltage output.

By way of non-limiting example, assuming that the value calculated atstep 605 may be calculated using a linear function that depends both onthe current and the voltage, e.g., using the equation: α=β*I+y*V; whereα is the calculated value, β and γ are coefficients (e.g., coefficientsthat are related to one or more parameter corresponding to elements ofthe power system, such as, resistance of one or more of the resistors inthe power system), I is the determined current, and V is the determinedvoltage. In cases where the determined current I is relatively highand/or the determined voltage V is relatively high, then as a result thevalue of α may be relatively high. If α is relatively high then thecalculated value α may be considered substantially greater than thereference value, and there may be a decrease in the voltage output. Incases where the determined current I is relatively low and/or thedetermined voltage V is relatively low, then as a result the value of αmay be relatively low. If α is relatively low then the calculated valueα may be considered substantially less than the reference value, andthere may be an increase in the voltage output.

By way of non-limiting numerical example, if the reference value is, forexample, about 1 v, and the determined current I is relatively high,e.g., about 10 mA, then the calculated value α may be about 1.5 v, whichis substantially greater than the reference value. As a result, theremay be a decrease in the voltage output, and as a result a decrease inthe determined current in the power system. If the determined current Iis relatively low, e.g., about 5 mA, then the calculated value α may beabout 0.5 v, which is substantially less than the reference value. As aresult, there may be an increase in the voltage output, and as a resultan increase in the determined current in the power system. In thisexample, if the determined current I is about 7.5 mA, then thecalculated value α may be about 1 v, which is substantially equal (e.g.,within a predetermined amount, within a measurable tolerance, etc.) tothe reference value. As a result, the voltage output may besubstantially maintained.

By way of another non-limiting numerical example, if the reference valueis, for example, about 0.75 v, and the determined current V isrelatively high, e.g., about 1 v, then the calculated value α may beabout 1.25 v, which is substantially greater (e.g., more than apredetermined amount, more than a measurable tolerance, etc.) than thereference value. As a result, there may be a decrease in the voltageoutput, and as a result a decrease in the determined voltage in thepower system. If the determined voltage V is relatively low, e.g., about0.25 mA, then the calculated value α may be about 0.5 v, which issubstantially less (e.g., less than by a predetermined amount, less thanby a measurable tolerance, etc.) than the reference value. As a result,there may be an increase in the voltage output, and as a result anincrease in the determined voltage in the power system. In this example,if the determined voltage V is about 0.5 v, then the calculated value αmay be about 0.75 v, which is substantially equal to the referencevalue. As a result, the voltage output may be substantially maintained.

Reference is now made to FIG. 6B which shows a flowchart of a method 651according to illustrative aspects of the disclosure. For example, method651 may be applied to power system 180 j of FIG. 5 in the descriptionthat follows. As an example, steps of method 651 may be implemented bycontrollers of system power devices 107, controllers of power devices103/103 a, and/or converters 110 acting as a primary controller.

At step 653, a current is determined (e.g., sensed).

For example, a current related to the voltage at terminal Vcpn of systempower device 107 may be measured, e.g., by current sensor 504. As anexample, the current flowing through resistor R1 may be measured. Inother examples, a different current may be measured or determined, forexample, the current through diode D1, the current through diode D2, thecurrent through switch Q2, etc. In some examples, the current may beestimated (e.g., by measuring current through inductor L1 and estimatingthe current through resistor R1 based on the measured current throughinductor L1 and the duty cycle of switch Q1).

At step 655, the current is compared to a reference current value.

If at step 655 it is determined that the current is substantially lessthan the reference current, then at step 657 the voltage output may beincreased. For example, the control unit 20, e.g., controller 200, maycontrol the converter 110, e.g., switch Q1 and/or switch Q2, to increasethe output voltage of the converter 110 that is output to terminal V−.This may control an increase in voltage at terminal Vcpn.

If at step 655 it is determined that the current is substantially equalto the reference current, then at step 659 the voltage output may bemaintained. For example, the control unit 20, e.g., controller 200, maycontrol the converter 110, e.g., switch Q1 and/or switch Q2, tosubstantially maintain the output voltage of the converter 110 that isoutput to terminal V−. This may maintain the voltage at terminal Vcpn.

If at step 655 it is determined that the calculated value issubstantially greater than the reference current, then at step 661 thevoltage output may be decreased. For example, the control unit 20, e.g.,controller 200, may control the converter 110, e.g., switch Q1 and/orswitch Q2, to decrease the voltage of the converter 110 that is outputto terminal V−. This may control a decrease in voltage at terminal Vcpn.

According to the present disclosure, a comparison of a calculated and/orsensed value to a desired and/or reference value may be done in order todetermine how to regulate a voltage in the power system, e.g., whetheror not the output voltage of a converter should be increased,maintained, or decreased.

As another example, it may be determined whether one or more sensedand/or calculated parameter is in a range of desired values in order todetermine how the output voltage should be regulated. For example, thisrange of desired values may be related to a range of voltage valuesand/or current values that are desired for operation of one or moresystem power devices 107.

As an example, this range of values may be represented as a look-uptable, e.g., stored in control unit 20, that may be used to helpdetermine a target output voltage for the converter, for example, basedon a determined current.

As another example, two separate control methods may be used. A firstcontrol method may adjust output voltage based on a determined voltage(e.g., measured at terminal V_(CP)), and a second control method mayadjust output voltage based on a determined current (e.g., measured onresistor R1). A controller may alternate between the two controlmethods, or may run both methods concurrently, for example, the firstmethod may be run at a first frequency, and the second method may be runat a different (higher or lower) frequency, for example, as to notinterfere with the first method.

Reference is now made to FIG. 7, which shows a voltage-current graphaccording to illustrative aspects of the disclosure. Graph 700illustrates a desired voltage value 702 and a desired current value 704.For example, desired voltage value 702 may be a desired voltage atterminal Vcpn, V+, V−, etc. For example, desired current value 704 maybe a desired current through resistor R1, or a different current. Graph700 also illustrates a voltage-current curve 706 indicative of arelationship between current values and voltage values. Voltage-currentcurve 706, or a section of voltage-current curve 706 may berepresentative of a range of desired values. As an example, the range ofdesired values may be determined by a range of desired voltage values,e.g., between a first low voltage, V_low, and a second high voltage,V_high, and/or a range of desired current values, e.g., between a firstlow current, I_low, and a second high current, I_high. As mentionedabove, relationships between current values and voltage values may beincluded in a look-up table, for example, stored in the control unit 20,e.g., memory 210, and used by the control unit 20, e.g., controller 200,to control the output of the converter 110. For example, thevoltage-current curve 706 may be used to help maintain a voltagesubstantially equal to, or within a certain range of, the desiredvoltage value 702 at similar terminals, e.g., terminals Vcpn, of aplurality of system power devices 107. For example, based on a currentsensed in the converter 110, e.g., a current flowing through resistorR1, the look-up table may be referenced, e.g., by control unit 20 and/orcontroller 200, and a target output voltage may be determined forregulating the voltage at terminal Vcpn based on the sensed current.This may help ensure that the voltage at one or more of the system powerdevices 107 does not increase to a point where it would cause one ormore other system power devices 107 to be bypassed or deactivated.

By way of non-limiting numerical example, assuming that a desiredvoltage on terminal Vcpn is 495 volts (v). Circuitry 500 may be utilizedto maintain voltage on terminal Vcpn for each system power device 107 ofsubstantially 495v. If the voltage representative of voltage on terminalVcpn indicates that the voltage on terminal Vcpn is greater than adesired voltage value and/or range of voltage values, then the voltagethat is output by controller 110 may be decreased to a reduced voltagewhich will decrease the voltage on terminal Vcpn.

Reference is now made to FIG. 8, which shows a power system 180 k,according to illustrative aspects of the disclosure. Power system 180 kincludes switch 802 which is operable to switch the power system 180 kbetween a daytime mode of operation and a nighttime mode of operation.Switch 802 is connected between converter 110 and terminal V−, with oneend of switch 802 connected to an output of converter 110 and a secondend of switch 802 connected to terminal V−. In some examples, switch 802may be switch SC and/or switch Q2 described above. Although illustratedseparately, it will be appreciated that switch 802 may be included aspart of converter 110 and/or system power device 107. In daytime mode,switch 802 is switched to the OFF position and converter 110 does notprovide any output voltage to terminal V−. In nighttime mode, switch 802is switched to the ON position and a voltage is applied to terminal V−above the potential of the ground connection provided by converter 110.One or more sensors may be used to help determine one or more parameterindicative of whether the switch should be switched to daytime mode ornighttime mode. The one or more sensors may include, for example: aclock, an irradiance sensor, a temperature sensor, a current sensor, avoltage sensor, a power sensor, etc. When one or more parameters fromthe one or more sensors indicate that the nighttime mode is appropriate,then switch 802 may be activated, e.g., by control unit 20 and/orcontroller 200. When one or more parameters from the one or more sensorsindicate that the daytime mode is appropriate, then switch 802 may bede-activated, e.g., by control unit 20 and/or controller 200. As anexample, the one or more parameters can be at least one of: a timevalue, an irradiance value, a temperature value, a current value, avoltage value, and a power value. Converter 110 may be configured tooutput a higher voltage when in nighttime mode as compared to daytimemode. For example, converter 110 may be configured to connect toterminal V− of a system power device 107 and to output about 5 v-10 v ifoperating in daytime operation mode, and to output tens or hundreds ofvolts if operating in nighttime operation mode, to increase expedite PIDreversion (e.g., to expedite discharge of charge stored on solar panelsduring the daytime).

According to some features, a topology of converter 110 may be selectedaccording to preferred time of operation. For example, a converter 110designed to operate primarily in daytime mode may be optimized to outputa low voltage (e.g., up to tens of volts), and a converter 110 designedto operate primarily in nighttime mode may be optimized to output ahigher voltage (e.g., hundreds of volts). Optimization to output ahigher voltage may include use of components rated for higher voltages,and/or use of magnetic elements (e.g. a transformer, for example, whereconverter 110 is a flyback, dual-active bridge, or different type ofisolating converter) to increase output voltage. As an example, thevoltage applied in a nighttime mode of operation can be in a range ofabout 100 volts to about 1000 volts, and the voltage applied in adaytime mode of operation can be in a range of about 10 volts to about150 volts.

In some cases, it might not be possible for power systems to havevoltage applied to terminals, e.g., V+, V−, etc., by converter 110during the day. For example, in some power systems, terminal Vcp mightbe grounded during the daytime, e.g. while system power device 107 isconnected to load 109. In such cases, after the load 109 is disconnectedfrom the system power device 107 at nighttime, then the switch 802 maybe activated in order to apply a voltage at terminal V− above thepotential of the ground connection provided by converter 110. In suchcases, the effects of PID might not be prevented during the daytime, butthe effects of PID on the system may be alleviated during the nighttime.

It will be appreciated that, in some cases, a relatively low outputvoltage may be applied at terminal V− in order to raise the potential atV− to above ground potential, e.g. an output voltage of about 5 v-10 v.In comparison, in some cases, a relatively high output voltage may beapplied at terminal V+ in order to raise the potential at V− to aboveground potential, e.g. an output voltage of hundreds of volts.Accordingly, an advantage of applying the output voltage at terminal V−,as opposed to terminal V+, may be that a substantially lower, relativelylow voltage may be applied by converter 110.

It should be understood that the steps in the flow charts of FIGS. 2B,6A, and 6B need not all be performed in the order specified and somesteps may be omitted, changed in order, or performed simultaneously.

According to one aspect of the presently disclosed subject matter thereis provided a method including:

determining a parameter related to a voltage value at a midpointterminal of a system power device; and

adjusting a voltage applied to a second terminal of the system powerdevice based on the parameter and a reference value, wherein the secondterminal is different from the midpoint terminal.

In addition to the above features, the method according to this aspectof the presently disclosed subject matter can include one or more offeatures (i) to (xxiii) listed below, in any desired combination orpermutation which is technically possible:

-   (i) wherein the midpoint terminal is one of a plurality of midpoint    terminals of the system power device.-   (ii) wherein the midpoint terminal is a terminal inside the system    power device.-   (iii) wherein the system power device is a direct current (DC) to    alternating current (AC) converter comprising a plurality of    capacitors connected in series between input terminals of the DC to    AC converter; and    -   the midpoint terminal is located between two of the plurality of        capacitors.-   (iv) wherein the second terminal is an input terminal of the system    power device.-   (v) wherein the input terminal is a negative voltage input terminal.-   (vi) wherein the parameter is a voltage value.-   (vii) wherein the parameter is a current value.-   (viii) wherein the reference value is a voltage value.-   (ix) determining a second parameter related to the voltage value at    the midpoint terminal of the system power device; and    -   adjusting the voltage applied to the second terminal of the        system power device based on the second parameter.-   (x) wherein the second parameter is a current value.-   (xi) wherein the second parameter is a voltage value.-   (xii) wherein the current value is related to a current in the    converter.-   (xiii) determining a third value based on the parameter and the    second parameter, and comparing the third value to the reference    value.-   (xiv) decreasing the voltage applied to the second terminal of the    system power device when the parameter is substantially greater than    a value related to the reference value.-   (xv) increasing the voltage applied to the second terminal of the    system power device when the parameter is substantially less than a    value related to the reference value.-   (xvi) substantially maintaining the voltage applied to the second    terminal of the system power device when the parameter is    substantially equal to a value related to the reference value.-   (xvii) determining a parameter related to a nighttime mode of    operation; and    -   applying the voltage to the second terminal of the system power        device based on the parameter related to the nighttime mode of        operation-   (xviii) a sensor configured to determine a parameter related to a    nighttime mode of operation; and    -   the converter is configured to apply the voltage to the second        terminal of the system power device based on the parameter        related to the nighttime mode of operation.-   (xix) wherein the voltage applied to the second terminal of the    system power device in the nighttime mode of operation is greater    than a voltage applied to the second terminal of the system power    device in a daytime mode of operation.-   (xx) switching between the nighttime mode of operation and the    daytime mode of operation based on the parameter related to the    nighttime mode of operation.-   (xxi) wherein the parameter is at least one of: a time value, an    irradiance value, a temperature value, a current value, a voltage    value, and a power value.-   (xxii) wherein the voltage applied in the nighttime mode is in a    range of about 100 volts to about 1000 volts.-   (xxiii) wherein the voltage applied in the daytime mode is in a    range of about 10 volts to about 150 volts.

According to another aspect of the presently disclosed subject matterthere is provided a device (e.g., an apparatus) including:

a sensor configured to determine a parameter related to a voltage valueat a midpoint terminal of a system power device; and

a converter configured to adjust a voltage applied to a second terminalof the system power device based on the parameter and a reference value,wherein the second terminal is different from the midpoint terminal.

This aspect of the disclosed subject matter can optionally include oneor more of features (i) to (xxiii) listed above, mutatis mutandis, inany desired combination or permutation which is technically possible

According to another aspect of the presently disclosed subject matterthere is provided a system including:

a sensor configured to determine a parameter related to a voltage valueat a midpoint terminal of a system power device; and

a converter configured to adjust a voltage applied to a second terminalof the system power device based on the parameter and a reference value,wherein the second terminal is different from the midpoint terminal.

This aspect of the disclosed subject matter can optionally include oneor more of features (i) to (xxiii) listed above, mutatis mutandis, inany desired combination or permutation which is technically possible

According to another aspect of the presently disclosed subject matterthere is provided a method including:

determining a parameter related to a nighttime mode of operation; and

applying a voltage to a terminal of a system power device based on theparameter related to the nighttime mode of operation.

According to another aspect of the presently disclosed subject matterthere is provided a device including:

a converter configured to apply a voltage to a terminal of a systempower device when the device is in a nighttime mode of operation;

a sensor configured to determine a parameter related to the nighttimemode of operation; and

a switch configured to switch between the nighttime mode of operationand a daytime mode of operation based on the parameter related to thenighttime mode of operation.

According to another aspect of the presently disclosed subject matterthere is provided a system including:

a converter configured to apply a voltage to a terminal of a systempower device when the system is in a nighttime mode of operation;

a sensor configured to determine a parameter related to the nighttimemode of operation; and

a switch configured to switch between the nighttime mode of operationand a daytime mode of operation based on the parameter related to thenighttime mode of operation.

It may be noted that various connections are set forth between elementsherein. These connections are described in general and, unless specifiedotherwise, may be direct or indirect; this specification may be notintended to be limiting in this respect. Further, elements of onefeature may be combined with elements from other features in appropriatecombinations or sub-combinations.

All optional and preferred features and modifications of the describedfeatures and dependent claims are usable in all aspects taught herein.Furthermore, the individual features of the dependent claims, as well asall optional and preferred features and modifications of the describedfeatures are combinable and interchangeable with one another.

1. An apparatus comprising: a sensor configured to determine a parameterrelated to a voltage value at a midpoint terminal of a system powerdevice; and a converter configured to adjust a voltage applied to asecond terminal of the system power device based on the parameter and areference value, wherein the second terminal is different from themidpoint terminal.
 2. The apparatus according to claim 1, wherein thesystem power device is a direct current (DC) to alternating current (AC)converter comprising a plurality of capacitors connected in seriesbetween input terminals of the DC to AC converter; and the midpointterminal is located between two of the plurality of capacitors.
 3. Theapparatus according to claim 1, wherein the second terminal is anegative voltage input terminal of the system power device.
 4. Theapparatus according to claim 1, where the apparatus is configured to:decrease the voltage applied to the second terminal of the system powerdevice based on the parameter being greater than a value related to thereference value; or increase the voltage applied to the second terminalof the system power device based on the parameter being less than avalue related to the reference value.
 5. The apparatus according toclaim 1, further comprising: a second sensor configured to determine asecond parameter related to the voltage value at the midpoint terminalof the system power device; and the converter is configured to adjustthe voltage applied to the second terminal of the system power devicebased on the second parameter.
 6. The apparatus according to claim 5,wherein the apparatus is configured to: determine a third value based onthe parameter and the second parameter; compare the third value to thereference value; and adjust the voltage applied to the second terminalof the system power device based on the third value.
 7. The apparatusaccording to claim 5, wherein at least one of the parameter and thesecond parameter is a voltage value or a current value.
 8. The apparatusaccording to claim 5, wherein the second parameter is a value related toa current in the converter.
 9. The apparatus according to claim 1,wherein the reference value is a voltage value.
 10. The apparatusaccording to claim 1, further comprising: a third sensor configured todetermine a parameter related to a nighttime mode of operation; and theconverter is configured to apply the voltage to the second terminal ofthe system power device based on the parameter related to the nighttimemode of operation.
 11. The apparatus according to claim 10, wherein thevoltage applied to the second terminal of the system power device in thenighttime mode of operation is greater than a voltage applied to thesecond terminal of the system power device in a daytime mode ofoperation.
 12. The apparatus according to claim 11, further comprising aswitch configured to switch between the nighttime mode of operation andthe daytime mode of operation based on the parameter related to thenighttime mode of operation.
 13. The apparatus according to claim 11,wherein the parameter related to a nighttime mode of operation is atleast one of: a time value, an irradiance value, a temperature value, acurrent value, a voltage value, and a power value.
 14. The apparatusaccording to claim 11, wherein the voltage applied in the nighttime modeof operation is in a range of about 100 volts to about 1000 volts, andthe voltage applied in the daytime mode of operation is in a range ofabout 10 volts to about 150 volts.
 15. A system comprising: a systempower device; a sensor configured to determine a parameter related to avoltage value at a midpoint terminal of the system power device; and aconverter configured to adjust a voltage applied to a second terminal ofthe system power device based on the parameter and a reference value,wherein the second terminal is different from the midpoint terminal. 16.The system according to claim 15, wherein the system power device is adirect current (DC) to alternating current (AC) converter comprising aplurality of capacitors connected in series between input terminals ofthe DC to AC converter; and the midpoint terminal is located between twoof the plurality of capacitors.
 17. The system according to claim 15,wherein the second terminal is a negative voltage input terminal of thesystem power device.
 18. A method comprising: determining a parameterrelated to a voltage value at a midpoint terminal of a system powerdevice; and adjusting a voltage applied to a second terminal of thesystem power device based on the parameter and a reference value,wherein the second terminal is different from the midpoint terminal. 19.The method according to claim 18, wherein the system power device is adirect current (DC) to alternating current (AC) converter comprising aplurality of capacitors connected in series between input terminals ofthe DC to AC converter; and the midpoint terminal is located between twoof the plurality of capacitors.
 20. The method according to claim 18,wherein the second terminal is a negative voltage input terminal of thesystem power device.